Method And Device For Stopping And Starting The Engine Of Hybrid Vehicles

ABSTRACT

In a method and a device for engine stop/engine start of hybrid vehicles, which includes an internal combustion engine and an electric machine which is coupled to the internal combustion engine and is selectively able to be operated regeneratively or motively, the engine speed can be detected and compared to a limit speed to initiate the stopping of the engine in a hybrid vehicle using an automatic start/stop mechanism, and if the engine speed drops to the threshold speed, the engine is stopped, the electric machine being switched over into the motive or the regenerative operation when the limit speed is reached; the electric machine assuming the limit speed, whereas the fuel supply of the internal combustion engine is shut down or remains shut down and the electric machine initiates the stopping of the internal combustion engine.

FIELD OF THE INVENTION

The present invention relates to a method and a device for stopping andstarting the engine of hybrid vehicles.

BACKGROUND INFORMATION

In vehicles having hybrid drive, the internal combustion engine is shutdown, as a rule, during standstill phases via an appropriate start-stopfunction for a broadened savings in fuel consumption. Since hybridvehicles have electric motors of clearly greater performance powerinstead of conventional starters, it is possible to have great comfortduring an automatic engine start after a start-stop phase.

The automatic stop operation in hybrid vehicles is generally initiatedonly when the engine is within the range of idling speed or has reachedit. However, because of this, the internal combustion engine isintercepted from a deceleration fuel cutoff, that was possibly initiatedpreviously, by the idle-speed controller above the idling speed (restartspeed), and is brought down to the required idling speed. This isrequired, since after falling below the restart speed, the engine speedwould drop off in an uncontrolled manner, and stalling would occur inthe worst case. Besides stressing the bearings, such a jolting shutdownis not desirable from a comfort point of view. this procedure reducesthe maximum consumption advantage that can be achieved by the stopoperation of the internal combustion engine by the duration of theactive idle-speed controller.

SUMMARY

Example embodiments of the present invention may provide a method and adevice for engine stop/engine start of hybrid vehicles by which, atuniform or increased comfort, the use of fuel may be reduced.

For this design approach, when it reaches a limit speed, the electricmachine is switched over into motive or regenerative operation, theelectric machine taking up the limit speed, whereas the fuel supply ofthe internal combustion engine is cut off or remains cut off, and theelectric machine carries the internal combustion engine over into theengine stop. Because of the taking up of the engine speed by theelectric machine, the engine speed may be regulated specifically tozero, because of which the internal combustion engine does not have tobe fired. It should be noted in this context that the limit speed, atwhich the electric machine takes up the engine speed, may also lie aboveor below the restart speed. The electric machine may take up the enginespeed in regenerative operation, since recuperation energy may still begained thereby.

The engine stop of the internal combustion engine may be performed viathe electric machine in a torque controlled or speed controlled manner.

The shut down position of the internal combustion engine may bespecifiably adjustable by the regulation of the angle of revolution ofthe electric machine. From this, the position of the cylinder of theinternal combustion engine is known, so that a restart of the internalcombustion engine may be simplified.

The restart of the internal combustion engine after the initiation of anautomatic stop operation may be accomplished by various methods. Thus,in vehicles having automatic transmissions, the release of the brakepedal or the operation of the accelerator may be used as a signal forthe restart. However, it should be ensured by the transmission controlthat no gear has been engaged or that there is no force locking in anautomatic clutch unit. In a vehicle having a manual shift transmission,the starting procedure may be initiated by stepping on the clutch pedal.In this instance, before the beginning of the starting procedure, itshould be ensured that the clutch is fully separated and/or that no gearis engaged, which may be recorded, for instance, using a gear sensor.

In order to make use of as great as possible a fuel consumption savingeven in stop operation, it is further provided not to execute therestart of the internal combustion engine already at the beginning ofthe clutch operation “clutch is opening” but rather only upon thedetection of “clutch is closing”. This distinction may be ensured, forexample, by a so-called interlock switch, both the clutch position“clutch fully open” and “clutch fully closed” being detected. Because ofthis, even in a vehicle at standstill and completely floored clutch(e.g., at a traffic light stop) the maximum usage advantage may beimplemented, in which the internal combustion engine is started onlywhen the driver releases the clutch pedal.

The inverter of the electric machine may be already activated when theclutch is opened, and the magnetization current of the electric machinemay be built up to a freely applicable value or to a maximum requiredvalue for the start. The engine starting procedure is able to take placerelatively simultaneously with the closing of the clutch.

The electric machine may be arranged as a crankshaft starter-generator,in order better to be able to intercept the torques occurring inresponse to the taking up of the engine speed.

The control of the internal combustion engine and the electric machinemay be accomplished via a control unit. In this context, the function isable to be integrated into the control unit of the internal combustionengine or the electric machine. However, it is also possible to providea separate control unit.

Example embodiments of the present invention are described below withreference to the appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a curve of the speed n_(mot) plotted against time tin the case of an engine stop having an automatic start-stop system(e.g., a conventional system).

FIG. 2 illustrates a curve of the speed n_(mot) in the engine stopaccording to an example embodiment of the present invention.

DETAILED DESCRIPTION

A conventional system is described with reference to FIG. 1. Before timet₁, a deceleration fuel cutoff is present, that is, the internalcombustion engine is no longer fired. Along with that, engine speedn_(mot) falls off up to time t₁ to a restart speed n_(W). When restartspeed n_(W) is reached, the internal combustion engine is switched onagain, and the engine speed is brought back to idling speed n_(LL) viathe idle-speed controller, which is achieved at time t₂. Only after idlespeed n_(LL) has been reached, at time t₂ the internal combustion engineis shut down, and engine speed n_(mot) falls off to zero in anunregulated manner up to time t₃.

FIG. 2 illustrates a method according to an example embodiment of thepresent invention. The internal combustion engine is again indeceleration fuel cutoff, in this context, speed n_(mot) falling off upto time t₁ to restart speed n_(W) or to a freely selectable value forthe limit speed. At time t₁ the electric machine is then switched to themotive or regenerative operation, and assumes speed n_(W) or the freelyselected limit speed. Thereafter, the electric machine regulates enginespeed n_(mot) in a speed regulated or torque regulated manner up to timet₄, t₄ being, e.g., less than t₃. In this context, the speed regulationtakes place specified by the rotation angle regulation of the electricmachine, so that the exact shutoff position of the internal combustionengine is known at time t₄.

1-15. (canceled)
 16. A device for an engine stop/engine start of ahybrid vehicles, comprising an internal combustion engine; an electricmachine coupled to the internal combustion engine, the electric machineselectively operable regeneratively or motively, an engine speedrecordable to initiate an engine stop in a start/stop automatic systemand comparable to a limit speed; wherein the device is adapted toinitiate the engine stop in response to a decrease of the engine speedto the limit speed, the device configured to switch over the electricmachine into one of (a) a motive operation and (b) a regenerativeoperation when the limit speed is reached; the electric machine adaptedto assume the limit speed, the device configured to at least one of (a)shut down and (b) remain shut down a fuel supply of the internalcombustion engine, the electric machine adapted to carry the internalcombustion engine over into the engine stop.
 17. The device according toclaim 16, wherein the motor stop of the electric machine is adapted totake place in at least one of (a) a torque-regulated and (b) aspeed-regulated manner.
 18. The device according to claim 16, wherein ashutdown position of the internal combustion engine is specifiablyadjustable by regulation of an angle of rotation.
 19. The deviceaccording to claim 16, wherein a pedal activity is recordable to restartthe internal combustion engine, the electric machine adapted to restartthe internal combustion engine as a function of the pedal activity. 20.The device according to claim 19, wherein, in a vehicle having amanually operated transmission, the operation of the clutch isrecordable.
 21. The device according to claim 20, wherein a startingprocedure is adapted to take place in response to a closing of a clutch.22. The device according to claim 21, wherein an inverter of theelectric machine is activatable in response to an opening of the clutch,and the magnetization current of the electric machine is built up. 23.The device according to claim 16, wherein the electric machine includesa crankshaft starter/generator.
 24. A method for an engine stop/enginestart of a hybrid vehicle including an internal combustion engine and anelectric machine coupled to the internal combustion engine, the electricmachine selectively operable regeneratively or motively, an engine speedrecordable to initiate an engine stop in a start/stop automatic systemand comparable to a limit speed, comprising: initiating the engine stopin response to a decrease of the engine speed to the limit speed;switching over the electric machine into one of (a) a motive operationand (b) a regenerative operation when the limit speed is reached, theelectric machine assuming the limit speed; at least one of (a) shuttingdown and (b) remaining shut down a fuel supply of the internalcombustion engine; and carrying the internal combustion engine into theengine stop by the electric machine.
 25. The method according to claim24, wherein the motor stop of the electric machine takes place in atleast one of (a) a torque regulated and (b) a speed regulated manner.26. The method according to claim 24, further comprising specifiablyadjusting a shutdown position of the internal combustion engine byregulation of an angle of rotation.
 27. The method according to claim24, further comprising: recording a pedal activity for restarting theinternal combustion engine; and restarting the internal combustionengine by the electric machine as a function of the pedal activity. 28.The method according to claim 27, further comprising recording operationof a clutch in a vehicle having a manually operated transmission. 29.The method according to claim 28, further comprising performing therestarting procedure in response to a closing of the clutch.
 30. Themethod according to claim 29, further comprising: activating an inverterof the electric machine in response to an opening of the clutch; andbuilding up a magnetization current of the electric machine.